Caption: Trichomonas vaginalis parasites, light microscopy. T. vaginalis is a protozoan that inhabits the human urogenital tract, causing the sexually transmitted infection trichomoniasis. The disease is typically symptomless in men, many of whom carry it without knowing. In women it can cause inflammation of the urethra, vagina and cervix, and a foul-smelling discharge. The individual protozoa are pear-shaped, and measure some 9x7 micrometres. Treatment is with a drug such as metronidazole. Filmed with differential interference contrast illumination.